The invention relates to improved processing olefin copolymers having a plurality of substantially linear branches and to compositions comprising them.
Ethylene copolymers are a well-known class of olefin copolymers from which various plastic products are now produced. Such products include films, fibers, and such thermomolded articles as containers and coatings. The polymers used to prepare these articles are prepared from ethylene, optionally with one or more additional copolymerizable monomers. Low density polyethylene (xe2x80x9cLDPExe2x80x9d) as produced by free radical polymerization consists of highly branched polymers where the branches occur randomly throughout the polymer, that is on any number of formed segments or branches. The structure exhibited easy processing, that is polymers with it could be melt processed in high volumes at low energy input. Machinery for conducting this melt processing, for example extruders and film dies of various configurations, was designed into product finishing manufacturing processes with optimal design features based on the processing characteristics of the LDPE.
However, with the advent of effective coordination catalysis of ethylene copolymers, the degree of branching was significantly decreased, both for the now traditional Ziegler-Natta ethylene copolymers and those from the newer metallocene catalyzed ethylene copolymers. Both, particularly the metallocene copolymers, are essentially linear polymers, which are more difficult to melt process when the molecular weight distribution (MWD=Mw/Mn, where Mw is weight-average molecular weight and Mn is number-average molecular weight) is narrower than about 3.5. Thus broad MWD copolymers are more easily processed but can lack desirable solid state attributes otherwise available from the metallocene copolymers. Thus it has become desirable to develop effective and efficient methods of improving the melt processing of olefin copolymers while retaining desirable melt properties and end use characteristics.
The introduction of long chain branches into substantially linear olefin copolymers has been observed to improve processing characteristics of the polymers. Such has been done using metallocene polymers where significant numbers of olefinically unsaturated chain ends are produced during the polymerization reaction. See, e.g., U.S. Pat. No. 5,324,800. The olefinically unsaturated polymer chains can become xe2x80x9cmacromonomersxe2x80x9d or xe2x80x9cmacromersxe2x80x9d and, apparently, can be re-inserted with other copolymerizable monomers to form the branched copolymers. International publication WO 94/07930 addresses advantages of including long chain branches in polyethylene from incorporating vinyl-terminated macromers into polyethylene chains where the macromers have critical molecular weights greater than 3,800, or, in other words contain 250 or more carbon atoms. Conditions said to favor the formation of vinyl terminated polymers are high temperatures, no comonomer, no transfer agents, and a non-solution process or a dispersion using an alkane diluent. Increase of temperature during polymerization is also said to yield xcex2-hydride eliminated product, for example while adding ethylene so as to form an ethylene xe2x80x9cend capxe2x80x9d. This document goes on to describe a large class of both monocyclopentadienyl and biscyclopentadienyl metallocenes as suitable in accordance with the invention when activated by either alumoxanes or ionizing compounds providing stabilizing, noncoordinating anions.
U.S. Pat. Nos. 5,272,236 and 5,278,272 describe xe2x80x9csubstantially linearxe2x80x9d ethylene polymers which are said to have up to about 3 long chain branches per 1000 carbon atoms. These polymers are described as being prepared with certain monocyclopentadienyl transition metal olefin polymerization catalysts, such as those described in U.S. Pat. No. 5,026,798. The copolymer is said to be useful for a variety of fabricated articles and as a component in blends with other polymers. EP-A-0 659 773 A1 describes a gas phase process using metallocene catalysts said to be suitable for producing polyethylene with up to 3 long chain branches per 1000 carbon atoms in the main chain, the branches having greater than 18 carbon atoms.
Reduced melt viscosity polymers are addressed in U.S. Pat. Nos. 5,206,303 and 5,294,678. xe2x80x9cBrushxe2x80x9d polymer architecture is described where the branched copolymers have side chains that are of molecular weights that inhibit entanglement of the backbone chain. These branch weight-average molecular weights are described to be from 0.02-2.0 MeB, where MeB is the entanglement molecular weight of the side branches. Though the polymers illustrated are isobutylene-styrene copolymers, calculated entanglement molecular weights for ethylene polymers and ethylene-propylene copolymers of 1,250 and 1,660 are provided. Comb-like polymers of ethylene and longer alpha-olefins, having from 10 to 100 carbon atoms, are described in U.S. Pat. No. 5,475,075. The polymers are prepared by copolymerizing ethylene and the longer alpha-olefins which form the side branches. Improvements in end-use properties, such as for films and adhesive compositions are taught.
The invention is directed to a polymer composition comprising essentially saturated hydrocarbon polymers having: A) a backbone chain; B) a plurality of essentially hydrocarbon sidechains connected to A), said sidechains each having a number-average molecular weight of from 2,500 Daltons to 125,000 Daltons and an MWD by SEC of 1.0-3.5; and, C) a mass ratio of sidechains molecular mass to backbone molecular mass of from 0.01:1 to 100:1. These invention compositions comprise essentially saturated hydrocarbon polymers having: A) a Newtonian limiting viscosity (xcex70) at 190xc2x0 C. at least 50% greater than that of a linear olefinic polymer of the same chemical composition and weight average molecular weight, preferably at least twice as great as that of said linear polymer, B) a ratio of the rubbery plateau modulus at 190xc2x0 C. to that of a linear polymer of the same chemical composition less than 0.5, preferably  less than 0.3, C) a ratio of the Newtonian limiting viscosity (xcex70) to the absolute value of the complex viscosity in oscillatory shear (xcex7*) at 100 rad/sec at 190xc2x0 C. of at least 5, and D) a ratio of the extensional viscosity measured at a strain rate of 1 secxe2x88x921, 190xc2x0 C., and time=3 sec (i.e., a strain of 3) to that predicted by linear viscoelasticity at the same temperature and time of 2 or greater. The invention polymers exhibit highly improved processing properties, improved shear thinning properties and melt strength.